It has long been the objective in sound reproduction to have the reproduction as spectrally accurate and realistic as possible. In almost all cases, the reproduction of sound is accomplished by electro-acoustic transducers. Generally, these transducers are comprised of a voice coil which converts an electrical signal to an oscillatory motion in a diaphragm. The diaphragm acts to transfer the oscillatory energy to the surrounding medium, thus producing an audible sound.
It is well known that current electro-acoustic transducers do not ensure correct retransmission of sounds. Specifically, distortion caused by standing wave phenomena and intermodulation distortion result in erroneous sound reproduction.
A standing wave can be described as the summation of two waves of the same frequency traveling in opposite directions. Typically, standing waves are generated when a propagating wave in a medium is reflected by a discontinuity in the medium. The reflected wave combines with the main propagating wave to form a standing wave. A medium subject to standing wave phenomena will exhibit standing waves having frequencies determined by the initial propagating wave frequency, and the physical characteristics of the particular medium.
In musical instruments, these standing wave resonances can be heard as the "voice" of the instrument. In electro-acoustic transducers, these standing waves tend to manifest themselves as harmonics of the base frequencies, and distort the overall quality of the sound reproduction. Furthermore, the newly formed harmonic frequencies act to cause intermodulation distortion, which can best be described as the nonlinear combination of differing frequencies with one another to produce frequencies equal to the sums and differences of the original frequencies. It can be seen that because of these additional frequencies, the original signal is corrupted. Thus, the reduction or elimination of standing waves from vibrating areas will remove a large portion of the harmonic and intermodulation distortions occurring in electro-acoustic transducers. This can be done by removing the discontinuity, or by removing the effects of the discontinuity.